Highly cis 1,4-regulated polybutadiene and 1,4-regulated polyisoprene are two kinds of synthetic rubbers with superior compositive performances, which finds wide applications in civil application, automobile, airplane manufacturing, aviation or the like. Specifically, when the cis 1,4-content in the structure of polyisoprene is high as 99%, the performance of the polyisoprene can compare with that of a natural rubber. Since 1960s when a rare earth metal compound for catalyzing diene polymerization is invented for the first time in China, large numbers of rubber companies have developed a series of catalyst systems on this basis and applied a series of patents. As compared with the catalyst systems based on other metals such as titanium, nickel or the like, the rare earth metal catalyst system is superior in catalytic activity and cis 1,4-selectivity for the polymerizations of isoprene and butadiene. Additionally, the obtained polyisoprene and polybutadiene rubbers have excellent compositive performances, such as the features of less gel, easy processability, wearing resistance, tearing resistance and highly crude rubber strength or the like. However, the formulations of the catalyst systems disclosed in these patents generally use rare earth metal carboxylates as the major catalysts, and are approximately divided into: insoluble bi-component systems, for example, neodymium chloride/a Lewis acid such as an alcohol, an amine, phosphoric acid or the like; soluble three-component neodymium-containing systems, for example, a neodymium carboxylate/an alkylating reagent (such as, an aluminum alkyl)/halide; and the recently developed four-component catalyst systems, for example, a neodymium carboxylate/an alkylating reagent (such as, an aluminum alkyl)/an alkyl halide/a conjugated monomer. For example, the catalyst system used for rubbers having wet-sliding resistant and low rolling resistance developed by Japan JSR. Company is composed of the reaction product of a Lewis base and a rare earth metal compound, an aluminoxane, an aluminum alkyl, and a metal chloride which are reactive with the Lewis base (U.S. Pat. No. 4,468,496 (1985)); the selectivity of butadiene cis 1,4-polymerization catalyzed by using a rare earth metal metal carboxylate/an aluminoxane/a metal chloride is not excess 90%, and the molecular weight distribution is relatively wide (<4.0) (U.S. Pat. No. 6,391,990 B1 (2002), U.S. Pat. No. 6,838,526 B1 (2005), US 200310065083A1, US 2005/0009979 A1). The catalyst systems of a rare earth metal phosphate/an alkylating reagent/a halogen donor or a rare earth metal phosphate/an alkylating reagent/a halogen donor/a conjugated monomer applied by French Mechelin Company can catalyze diene polymerization, wherein the cis 1,4-selectivity is increased to 98% or more. However, in order to realize a cis 1,4-selectivity more than 99%, the polymerization temperature should be lowered to −55° C., and additionally, the rubber has a Mooney point of 80 or less at 100° C. (U.S. Pat. No. 6,838,534 B2 (2005), U.S. Pat. No. 6,858,686 B2 (2005) U.S. Pat. No. 6,949,489 B1 (2005), U.S. Pat. No. 6,992,157 B2 (2006)). The patent applications U.S. Pat. No. 6,713,565 B2, U.S. Pat. No. 7,022,783B2 (2006), US H2036H (2002) and US 2005/0137338A1 (2005) by the Goodyear Tire & Rubber Company relate to a catalyst system of a neodymium carboxylate/an aluminum alkyl/a halogen-containing compound/a conjugated monomer, which can catalyze the highly cis 1,4-polymerization of isoprene or the random copolymerization of isoprene and butadiene, wherein the cis 1,4-selectivity can be 98% or more. A catalyst system of a rare earth metal metallocene/an aluminum alkyl/an organic boron salt cations applied by the researchers of Riken has very highly catalytic activity on the homopolymerization of a conjugated olefine and the copolymerization of a conjugated olefine with a halogen-containing olefine, and additionally, the polymerization reaction is characterized by livingness mode (US 2002/0119889, U.S. Pat. No. 6,596,828 (2003), U.S. Pat. No. 6,960,631 B2, U.S. Pat. No. 6,683,140 B2). However, in order to obtain a cis 1,4-selectivity of 95% or more, the reaction must be performed at a polymerization temperature below −20° C.
The inventors have found a three-component cationic type catalyst system composed of a NCN-diimine pincer type rare earth metal halide, an aluminum alkyl and an organic boron salt, which has a cis 1,4-selectivity above 98% on butadiene or isoprene polymerization and this cis 1,4-selectivity can be maintained in a temperature range of 20-80° C. The catalytic efficiency of the catalyst system is about 20%. The above described catalyst system is completely different from any one of the catalyst systems reported previously (Reference: Wei Gao, Dongmei Cui, J. Am. Chem. Soc. 2008, 130, 4984-4991; Chinese Patent 200710056309.2).